The present invention relates generally to material handling implements, and more specifically to an improved control system for automatically positioning the boom of a material handling implement at a desired angular position with respect to the frame.
Backhoe units presently in commercial use include an articulated boom that is pivoted about a vertical pivot axis on a vehicle. The boom is usually pivoted on the vehicle by fluid rams and the outer end of the boom has a bucket supported thereon that is pivoted by a further fluid ram.
Hydraulically operated backhoes of the above type require constant attention of the operator to perform the various functions. For example, in a normal trenching operation, the operator must continually position the attitude of the bucket with respect to the trench and perform the digging operation by the manipulation of several manually actuated control valves. After the bucket has been filled, the operator must then raise the bucket above ground level and pivot the boom with respect to the frame so that the bucket can be dumped in a position adjacent the trench. In such an operation, the operator must continuously operate numerous levers to carry out the necessary sequence of operation. Throughout each step of the digging process, the operator must make continual decisions as to the necessary attitudes and movements of the components of the backhoe and actuate control valves at the appropriate time to direct the digging and dumping cycles. For these reasons, considerable time is required to train a skillful backhoe operator. Even after the skill is acquired, the work is demanding and tiring, requiring continuous mental and physical alertness to maintain maximum digging rates.
In recent years numerous proposals have been made for automating various portions of a cycle of operation for a backhoe. For example, Caywood et al. U.S. Pat. Nos. 3,339,763 and 3,414,146 disclose completely hydraulic circuits that will function to automatically perform certain functions of a backhoe cycling operation in response to pressure changes in the various fluid motors that are utilized to manipulate the boom and the bucket. One of the problems with control systems of this type is that they are extremely complicated in nature. Furthermore, the flexibility of the operations that can be performed is extremely restricted since there is very little provision for changing the parameters of the automatic control cycle.
More recently, it has been proposed to utilize electric control systems for actuating the swing control valve in a backhoe unit. This type of system is disclosed in Carlson et al. U.S. Pat. No. 3,698,580. While this type of system utilizes an electrical circuit for controlling the position of the boom with respect to the vehicle, such a system has an inherent shortcoming in that it requires the operator to set the desired position for the swing tower, each time it is to be moved.